Thick film resistor compositions widely used in thick film resistor electrical parts, thick film hybrid circuits, etc. are compositions for preparing a resistor thick film by printing the composition on a conductor pattern or electrodes formed on the surface of an insulating substrate, followed by firing the print at temperatures near 850° C.
The thick film resistor compositions are prepared by dispersing a conducting component and an inorganic binder in an organic medium (vehicle). The conducting component plays a role in determining the electrical properties of the thick film resistor, and a ruthenium oxide may be used as this component. The inorganic binder comprises glass, and has a function of retaining the thick film integrally and binding it to the substrate. The organic medium is a dispersing medium that affects the application properties, particularly rheology, of the composition.
Recent increases in the price of ruthenium have made lower ruthenium compositions desirable. One approach is to reduce the amount of ruthenium that is necessary in a composition by using higher surface area ruthenium oxides, but this results in temperature coefficients of resistance (TCR) becoming more negative. At times, the TCR exceeds the permissible range, especially in the sheet resistivity range of 10 Kohm-1 Megohm. It is desirable for a thick film resistor composition to have a low ruthenium content while maintaining positive TCR.